1. Field of the Invention
The present invention relates to a communication device and a communication system.
2. Related Background Art
Remarkable progress has been made in wireless communication technology in recent years. A third generation mobile communication system based on a wideband code division multiple access (W-CDMA) system and called International Mobile Telecommunications-2000 (IMT-2000) forms a communication network capable of data transfer at a rate of 384 kbps in a mobile communication environment.
An international standardization organization called Third Generation Partnership Project (3GPP) advances a process of standardizing IMT-2000 and successively releases the IMT-2000 standard specification, which are made public on a web site (http://www.3gpp.org/) or through other media.
Further, IMT-2000 is the first system having introduced therein a user identification module called a Universal Subscriber Identify Module (USIM). A right granted to a user to use a portable telephone, which is conventionally assigned to the portable telephone by user subscription, is incorporated in one USIM. The user can use any of a plurality of communication units under the same user subscription by attaching the USIM to the communication unit.
Meanwhile, in digital cameras, image data is generally managed in accordance with a standard called Design rule for Camera File system (DCF). DCF is an image file format standard prescribed in JEIDA-492-1998 by Japan Electronic Industry Development Association (JEIDA). Image data to be stored is compressed into a DCF file by JPEG (Joint Photographic Experts Group) compression.
Here, JPEG compression is an image coding method for compressing image data in such a manner that original image data undergoes discrete cosine transform on a predetermined block basis to be converted into data per frequency components, and data components of little visual influence in maintaining image quality are removed from the image data.
Conventionally, an image communication system is known in which an image photographed with a digital camera is transferred to a computer in a remote location by wireless communication through a communication line.
In a digital camera used in such a conventional image communication system, data on a photographed image is transferred to an internal frame memory, the data in the frame memory is JPEG-compressed by an internal CPU, and the compressed data is stored in DCF format in a memory card. An operator operates the camera to transfer the stored image data from a wireless communication unit to an image server to store the data in the same.
FIG. 2 shows a format of the image data to be transferred at this time. Referring to FIG. 2, a portion 201 is SOT (Start Of Transmission) designating the beginning of a transferred frame; a portion 202 is transfer length information indicating the length of the transferred frame, a portion 203 is SOI (Start Of Image) designating the beginning of the DCF data; a portion 204 is APP1 information (e.g., date and time information) in accordance with the DCF standard; a portion 205 is JPEG compressed image data in accordance with the DCF standard; a portion 206 is EOI (End Of Image) information designating the end of the DCF data; and a portion 207 is EOT (End Of Transmission) designating the end of transferred data.
Information between SOI information 203 and EOI information 206 is the DCF data in accordance with the DCF standard.
In the above-described conventional image communication system, an entire image photographed with the digital camera is transferred to an image server and no information on the transferred image is left on the digital camera side.
When image data is transferred from the image server, APP1 information (e.g., date and time information) about image data stored in the image server is transferred to the digital camera side by an operation on the digital camera side to be checked. The operator selects necessary image data by referring to the date and time information. The selected information is transferred to the digital camera to enable the operator to view the image.
In the above-described conventional system, however, only the date and time information can be referred to on the digital camera side as information for identification of images, which is transferred from the image server. Therefore, the operator cannot check whether a transferred image is an image selected by the operator until the corresponding image data is transferred and displayed. If images other than the selected image are transferred, transfer time and communication cost for the operation are wasted.
In a case where the image server is shared by a plurality of persons, images other than those transferred by one person may be stored in the image server. In such a situation, the above-described problem is more serious.
Situations in which the above-described problem may arise are not limited to the case of transfer of images photographed with the digital camera to the image server. That is, there arises also the same problem in a case where an image stored in a personal computer is erased after the image has been transferred from the personal computer to an image server.
The problem of difficulty in selecting an image to be viewed by referring to the date and time information is not limited to the case where a person who transferred an image to an image server views the image by himself or herself. There arises also the same problem in a case where some other person wishes to view the image.